1. Field of the Invention
The present invention relates to a brushless motor, and, more particularly, to a brushless motor which can avoid the activation failure at the time it is activated.
2. Description of the Related Art
In general, a brushless motor has a housing and a rotor which is rotatable in relative to this housing. An annular rotor magnet is attached to this rotor, and a stator is attached to the housing, facing the rotor. The stator has a stator core and a drive coil wound around a plurality of teeth of the stator core. As the required current is supplied to the drive coil, the rotor rotates.
A uni-phase bipolar driving system is known as a driving system for such a brushless motor. According to this driving system, one drive coil is wound around all the teeth of the stator in the specified manner, and a drive current in a predetermined direction and a drive current in the opposite direction to this predetermined direction are alternately supplied to this drive coil. With regard to the stator, position detecting means like a Hall element is provided so that the current to be supplied to the drive coil is controlled on the basis of the output signal of the position detecting means.
In the conventional brushless motor which uses the uni-phase bipolar driving system, however, the generated driving torque has the characteristic curve of a pulsating current so that there is a dead point between peaks of the curve at which the value becomes substantially zero. At the time of the activation of the motor, therefore, the motor may fail to start due to this dead point.